07 Dec 2005
Heritage applications look set to benefit from a remote imaging and ablation system based on LIBS.
Three scientists in Sweden believe they are the first to combine remote imaging with laser-induced breakdown spectroscopy (LIBS). The trio has cleaned contaminated stone surfaces remotely using the system and says that it could aid restoration of important cultural heritage. (Optics Letters 30 2882)
The system, developed by Rasmus Grönlund, Mats Lundqvist and Sune Svanberg from Lund Institute of Technology, is housed in an 8 m long truck and is powered by a generator. It is based on a frequency-tripled Nd:YAG laser emitting 170 mJ, 4-5 ns pulses at 355 nm.
The pulses are passed through a custom-designed telescope and focused onto the remote target using a scanning mirror mounted on the roof of the truck. Light from the induced plasma is collected by a receiving telescope and analysed by a spectrometer equipped with an intensified CCD camera.
According to Grönlund, a key aspect is balancing the beam diameter and pulse energy to ensure that a plasma is created at the target without damaging the optics in the transmission system.
The team uses the same set-up to perform both imaging and ablation. "The beam is scanned across the target to perform imaging and ablation," Grönlund told Optics.org. "We scan for about 30 seconds to 1 minute at each point for imaging and at a speed about 10 cm2/min for ablation. We can choose the time to stay at each point depending on the degree of contamination [for ablation]."
The researchers parked their truck 60 meters away from an easily accessible roof where they placed several targets. A series of plates made from different metals was successfully imaged by looking at the characteristic lines emitted from each material. The team also removed dirt and algae from a garden statue as well as pencil markings on a marble ornament.